The present invention relates generally to a molten carbonate type electrolyte and more particularly relates to Li/Na and BaCaNaLi carbonate electrolytes. These electrolytes exhibit substantially reduced segregation and improved fuel cell performance.
Current molten carbonate fuel cells ("MCFC") contain a base mixture of about 62 mole percent ("m/o") Li.sub.2 CO.sub.3 and 38 m/o K.sub.2 CO.sub.3. When mixed with lithium aluminate, this mixture serves both as an electrolyte and gasketing for the fuel cell and stack. This system exhibits a broad liquidus range in its phase diagram but has several important drawbacks. When the fuel cell is operated at a high electrochemical load, segregation of the electrolyte occurs within each cell and also within a stack of the cells. Within the cell, segregation increases potassium concentration near the Ni(Li)O cathode, and this leads to increased solubility of the cathode as well as increased corrosion of the cell hardware. This progressive segregation and corrosion results in substantial decline of performance. In the stack of cells, a high voltage potential difference on the gaskets causes electrolyte segregation which floods one end of the bipolar stack while the other end is starved. This further leads both to decline of performance of end cells of the fuel cell and overall lifetime of the fuel cell. Attempts have been made to alleviate the problem by adding external electronic controls or by adding internal manifolding to make segregation more difficult.
In order to overcome some of these difficulties, a Li/Na carbonate of eutectic composition has been developed. However, this composition has a greater wetting ability then the Li/K, and cell performance is reduced to the electrolyte flooding of the electrode and reducing fuel contact area. These problems of segregation have been partially alleviated by altering the electrode structure and chemistry to accommodate the peculiarities of the eutectic Li/Na electrolyte.
Other efforts have been made to diminish segregation by adding BaCO.sub.3 or CaCO.sub.3 to Li/Na. However, during fuel cell operation, the Ba or Ca precipitated in the pores of the electrode causing reduction in efficiency and operational lifetime.
It is therefore an object of the invention to provide an improved fuel cell.
It is another object of the invention to provide a novel molten carbonate fuel cell (MCFC) having reduced electrolyte segregation and improved MCFC performance.
It is a further object of the invention to provide an improved MCFC containing an off-eutectic Li/Na electrolyte.
It is yet another object of the invention to provide a novel MCFC of about 60-75 mole percent Li in a Li/Na electrolyte.
It is an additional object of the invention to provide an improved MCFC having a LiNaBaCa carbonate electrolyte forming a low melting point eutectoid.
It is also a further object of the invention to provide a novel LiNaBaCa electrolyte composition with 2 to 5 m/o in both Ba and Ca.
It is another object of the invention to provide an improved MCFC electrolyte of Li/Na rare earths for reducing electrolyte segregation.
These and other objects and advantages of the invention will be readily apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings described below.